Seeking tips to drilling an absolutely dead-center hole w/drill press

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| Looking for any tips/tricks for drilling a hole w/a drill press that's as | close to dead-center to a specified point as possible. | | Here's what I've been doing - I have the position marked with graph paper | that's taped to the workpiece. With the help of a magnifying glass, I | painstakingly move the piece until the tip of the bit is aligned with the | conjoining lines. By aligning with the tip I mean I view the tip both from | the narrow or "pointy" persepective within the channel of the bit and then | turn it 90 deg and look at the the wider perspective, and view it from the | side and front to make sure I have it aligned with both the X and Y axis. | When I finally get it so the tip is as centered as I can make it whichever | way the bit is turned and in relation to both axis, I clamp the piece to the | plate of the drill press and drill the hole. However, on examination, the | hole comes out obviously not dead center in relation to the graph paper | lines. | | I've also tried aliging it with the drill running, going visually by where | the "point" appears to be when the bit is spinning. I get somewhat better | results this way but wonder if there's a more precise and dependable way of | achieving a centered hole. | | Thanks for any input.
Finding one of the optical center punches is the best way to locate the center punch hole. After that, find the smallest drill bit your press will handle and drill the hole with that, or at least a quarter of an inch or so. The next thing is hardware you have to go look for. Double margin drill bits. You work your way up using the previous hole size as the first margin, or pilot bit. Not sure where to some, industrial supply, ebay, aviation supply, or similar places. I've also used what we call "core drills" which are special drill bits made by turning down the first quarter of an inch or so of the drill bit to the pilot hole you're working with, but obviously not too small. You still have to sharpen the remaining edge of the bit. In doing this, I've started with a center punch mark and worked my way up to a 0.3125" +/- .002" which is even harder without the right tools. By the way, double margin drill bits are awesome for drilling stainless! I bought a bunch at Boeing surplus near Seattle and absolutely love using them.
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My ears are burning....
"Absolute" DOES NOT work in machining. There is _always_ a tolerance. Sorry for being obnoxious but when you start to get paid to do this work, tolerances are not a factor - they are life.
What is your application? Do you need your hole to be straight as well?
Others have given good advice. Do you have a combination square with a "center head"? These are specifically used to draw a line on the flat face of a cylinder which intersects the center of that cylinder (the line is a "diameter"). Drawing two such lines (three may be better if your stock is uneven about its diameter) will give you the center of your part.
Simply center punch (you may want to use a prick punch first), center-drill, pilot drill (if final diameter exceeds roughly 1/4"), drill, then ream if necessary.
While this will give you the location of the *top* of your hole, anything below the surface is a crap shoot and is severely dependant upon your knowledge and skill of setting up your part correctly, using appropriate tools and using good technique for drilling.
HTH.
Regards,
Robin
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I was surprised at the number of replies I got in such a short time. It occurred to me that I never said that I'm drilling into wood. I included the metalworking forum to see if there overlapping skills. I suppose I could clamp a piece of sheet metal over the spot and drill through it if that would help.
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Let me amend that, plexi that's been glued over wood.
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A great tool for dead-centering is available from Micro-Mark. It is a laser guide which is gripped in the chuck and projects a red dot onto the workpiece:
http://www.ares-server.com/Ares/Ares.asp?MerchantID=RET01229&Action Κtalog&Type=Product&IDƒ191
Of course, you will still need to centerpunch and/or use a center drill as outlined in the other responses. The laser guide just assures that the drill is aimed EXACTLY where it should be!
--
H. L. Law



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If you get better results when the drill press is running I think you have excessive runout in the quill. Put a long bit ,largest diameter the chuck will take, turn drill press on. Do you see any wobble? If you have a dial indicator and a length of drill rod, you can check runout better.Sometimes the chuck can be at fault, though probably not. mike
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_perfectly_ on-center holes in anything. A) any twist drill will tend to cut from a few tenths to a few thou oversized - partly due to lost motion in the system and imperfect grinding, and partly due to false edges and chips abrading the hole sides, and B) because any but a really stout drill that is _perfectly_ ground will tend to wander a bit during its cut.
When one must have holes centered to within a few "tenths", you need to pre-drill the hole a few (say 15-20) thousanths undersized (for chip relief and fast stock removal) on a milling machine, then re-index (or re-check your index of) the workpiece, and "drill" the hole with a fly cutter, finishing with a reamer.
For most work, this sort of accuracy isn't necessary. If your drill press spindle has more than a half-thou of runout, it needs servicing. If your bits drill more than two thousanths over their miked-out size, they need regrinding to center the cut. Short, stiff bits tend to wander less than long flexible ones.
LLoyd
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Indeed there is no such tool that exists...

Why do you recheck after drilling? If an axis of the mill is not moving while you are cutting, it must be clamped - always.

Perhaps you mean, "boring head"?

This depends on the diameter of the drill, of course...
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Yes. Just 'checking' never hurts a precision job.

Ummmm.... Blush... yep...

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wrote:

Have you tried making a little hole where you want to drill with a scratch awl first? You could set the bit right into the divot while the press is off, then clamp the piece in place and go to town.
Aut inveniam viam aut faciam
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